Internal combustion engine designs often seek to operate at relatively higher specific power levels in an effort to improve vehicle fuel efficiency. For example, to reduce engine displacement one may use a pressure charging system, such as a turbocharger, to maintain the power and torque of a relatively large engine, which may then improve the vehicle's fuel efficiency. When a relatively smaller engine displaces a larger engine in a given vehicle, the new vehicle may have better fuel economy due to the reduction in throttling losses, as a relatively smaller engine needs to open the throttle more to achieve similar torque as in a relatively larger engine. However, as the smaller engine may then operate at higher specific power levels, the efficiency gains may be reduced by the presence of knock. Knock is referenced within this application to the presence of detonation or auto-ignition, resulting from relatively high temperature conditions, which typically occur at high specific power levels, causing auto-ignition of unburned gases in the cylinder. Knock may produce objectionable noise and may also lead to catastrophic engine failure.
Engine lube oil is intentionally coated on a cylinder to reduce friction and prevent ring and liner wear. Some of this lubricant may therefore enter the boundary layer of the cylinder and the combustion chamber in the end gas region (the region of the last gas to burn). It may therefore be useful to evaluate (e.g. quantify) lubricant effects on engine knock performance which may then be used to identify lubricants yielding relatively lower fuel consumption, due to the ability of an engine to operate at relatively high compression ratios and/or closer to a point of maximum engine efficiency. It may also be useful to identify, for a given lubricant, the tendency of the oil to knock within a given fuel with respect to selected engine operating parameters, such as spark advance, compression ratio, intake air temperature, coolant temperature, oil temperature and/or peak torque at minimum advanced spark timing.